A model of solid-water-air coupling in triphasic mixtures is compared withsolid-water coupling in biphasic mixtures with an application to partially saturatedporous media. Based on thermodynamics, the mathematical frameworkgoverning the behavior of a partially saturated soil is derived usingbalance equations, and the numerical implementation and drainage tests ofa soil column are carried out to validate the obtained formulations. The roleof the air phase in the hydro-mechanical behavior of triphasic mixtures canbe analyzed from the interactions among multiple phases for the constitutivebehavior of a solid skeleton, and the triphasic mixture model can beapplied in geotechnical engineering problems, such as sequestration andair storage in aquifers.